1. Field of the Invention
The present invention relates to a fluorescent display apparatus constituting a large-screen display for use in a stadium or the like.
2. Description of the Prior Art
FIG. 1 is a sectional view showing a prior art fluorescent display apparatus disclosed, for example, in U.S. Pat. No. 4,893,056 and FIG. 2 is an exploded perspective view of the same. Referring to FIG. 1 and FIG. 2, reference numeral 1a denotes a display screen shaped in the form of a flat plate and having sixteen fluorescent display cells 8, 1b denotes a frame body forming side faces of a vacuum envelope of the fluorescent display apparatus, 8A denote accelerating anodes disposed so as to surround the fluorescent surface of the fluorescent display cells 8, 14 denotes a planar electrode as a first control electrode made in the form of a flat plate, and 1c denotes a substrate with such components as cathodes 4, second and third control electrodes 10, 12 , and their wiring leads 11, 13 disposed thereon, 40 denotes a lead. The fluorescent display apparatus is constructed by providing the planar electrode 14 in the space surrounded by the frame member 1b and by fixing the display screen 1a on one end of the frame body 1b and fixing the substrate 1c on the other end of the frame body 1b.
The display screen la is provided with sixteen fluorescent display cells 8 coated with phosphor and arranged in a matrix (4 rows by 4 columns) thereon. Each fluorescent display cell 8 is supplied with a high voltage and adapted to emit light by being bombarded with electrons. In the planar electrode 14, there are made sixteen openings 15 arranged in a matrix (4 rows by 4 columns) corresponding to the fluorescent display cells 8.
FIGS. 3(a) and 3(c ) are plan view showing electrode structure on the substrate 1c, in which the horizontal direction is the direction of the row and the vertical direction is the direction of the column. In the center of the substrate 1c, there is made an exhaust hole 2 used as the passage of exhaust air when evacuating the interior of the fluorescent display apparatus. There are four directly heated filament cathodes 4 disposed above the substrate 1c slightly spaced from its surface. When a heater current is passed through each cathode 4, thermoelectrons are emitted from the cathode 4.
On the surface of the substrate 1c at the portions corresponding to the cathodes 4, there are disposed eight data electrodes, in an array of 2 rows by 4 columns, as the second control electrodes for controlling thermionicemission of the cathodes 4. Each data electrode 10, by being supplied with positive or negative potential relative to the potential of the cathode 4, controls thermionicemission of each corresponding cathode 4. On the surface of the substrate 1c at both sides in the direction of the column of each data electrode 10, there are disposed eight scanning electrodes 12, in a matrix of 4 rows by 2 columns, as the third control electrodes for controlling the moving direction of the thermoelectrons emitted from the cathode 4.
The size of the data electrode 10 is made smaller than that of the scanning electrode 12. Of the eight data electrodes 10, two each arranged in the same column are connected together to each of four wiring leads 11 arranged in the direction of the column, and of the eight scanning electrodes 12, two each in the same row are connected together to each of the four wiring leads 13 arranged in the direction perpendicular to the wiring leads 11, that is, in the direction of the row. The wiring leads 11 and the wiring leads 13 are laid down with an insulating layer interposed therebetween so as not to come into contact with each other. These data electrodes 10, scanning electrodes 12, wiring leads 11, and wiring leads 13 are formed on the substrate 1c by printing.
Operation will be explained below. Referring to FIGS. 3(a), 3(b ) and 3(c) S1, S2, S3, and S4 indicate scanning signals
Applied to two each scanning electrodes 12 in the same row, and D1, D2, D3, and D4 indicate data signals applied to two each data electrodes 10 in the same column. FIG. 4 is a timing chart of the application of the signals S1 to S4, and D1 to D4. FIG. 5 is a diagram showing arrangement in a matrix of the fluorescent display cells 8 formed on the display screen 1a. Light emitted from each of the fluorescent display cells 8 is controlled by applying the signals S1 to S4, and D1 to D4.
The operation for controlling the emission of light will now be described.
ON (positive)/OFF (negative) control of each of the data electrodes 10 and ON (positive)/OFF (negative) control of each of the scanning electrodes 12 are performed at the timings of the data signals and scanning signals as shown in FIG. 4. There are four phases of periods in the combinations of the ON/OFF states of the scanning electrode 12 and the ON/OFF states of the data electrode 10 (i.e., where the state of the scanning electrode 12 and the data electrode 10 are ON and ON, ON and OFF, OFF and ON, and, OFF and OFF, respectively). The light emitting condition of the fluorescent display cell in each period will be described below. FIG. 6 and FIG. 7 are schematic diagrams showing states of potential in these four periods.
.circle.1
Where both the scanning electrode 12 and the data electrode 10 are in the ON state, the field in the vicinity of the heated cathode 4 becomes positive under the field of the data electrode 10 and the scanning electrode 12 and hence thermoelectrons are emitted. The emitted thermoelectrons are deflected under the field of the scanning electrode 12 and accelerated by the planar electrode 14 to advance to the corresponding fluorescent display cell 8 and bombard the fluorescent display cell 8. Then, the electrons coming into contact with the phosphor material cause the fluorescent display cell 8 to emit light (FIG. 6 .circle.1 ). .circle.2 Where the scanning electrode 12 is in the ON state and the data electrode 10 is in the OFF state, since the data electrode 10 is disposed closer to the cathode 4, the field of the data electrode 10 affects the cathode 4 more strongly. Hence, in this case, the field in the vicinity of the cathode 4 becomes negative so that the thermionicemission from the cathode 4 is suppressed and the fluorescent display cell 8 does not emit light (FIG. 7 .circle.2 ).
.circle.3 Where the scanning electrode 12 is in the OFF state and the data electrode 10 is in the ON state, although the data electrode 10 is positive, both the scanning electrodes 12 formed on both sides of the data electrode 10 are negative, and moreover, the size of the scanning electrode 12 is larger than that of the data electrode 10, and hence the field in the vicinity of the cathode 4 becomes negative so that the thermionicemission from the cathode 4 is suppressed and the fluorescent display cell 8 does not emit light (FIG. 6 .circle.3 ). .circle.4 Where both the scanning electrode 12 and the data electrode 10 are in the OFF state, the field in the vicinity of the cathode 4 becomes negative so that the thermionicemission from the cathode 4 is suppressed and the fluorescent display cell 8 does not emit light 10 (FIG. 7 .circle.4 ).
In the described manner, the emission of light in each of the fluorescent display cells 8 is controlled at will by combination of the potential of the data electrode 10 and the scanning electrode 12. Since, here, the potential of the data electrode 10 and the scanning electrode 12 is controlled by the data signals D1-D4 and the scanning signals S1-S4, it is made possible to have each of the fluorescent display cells 8 emitting light or not at will by controlling these signals.
Now, when two data electrodes 10, as adjoining two control electrodes, are simultaneously ON, two adjoining fluorescent display cells 8 corresponding thereto emit light, and when only one data electrode 10 is ON, only one of the fluorescent display cells 8 emits light. The difference in the light emission in the fluorescent display cells 8 between these cases is shown in FIG. 8(a) and FIG. 8(b), wherein four fluorescent display cells 8a, 8b, 8c, and 8d controlled by ON/OFF states of the corresponding two data electrodes 10a and 10b and two scanning electrodes 12a and 12b are shown. When the data electrodes 10a and 10b are both turned ON (positive potential) and the scanning electrode 12a is turned 0N (positive potential), thermoelectrons from the cathode 4 are deflected by the field of the scanning electrode 12a as shown in FIG. 8(a) and bombard the corresponding two fluorescent display cells 8a and 8b causing these two to emit light.
On the other hand, when only the data electrode 10b and the scanning electrode 12a are ON, the thermoelectrons are deflected so as to bombard only one fluorescent display cell 8b, as shown in FIG. 8(b), causing the same to emit light. In this way, by controlling the states of potential developed also by the other scanning electrodes 12a and 12b and the data electrodes 10a and 10b, one to four of the fluorescent display cells 8a to 8d can be selectively caused to emit light.
Since the prior art fluorescent display apparatus is constructed as described above, when only one each electrode, i.e., the data electrode 10b and the scanning electrode 12a, are turned ON, the data electrode 10a is held negative, and this causes the region of thermionicemission on the cathode 4 to reduce to about one half as shown in FIG. 8(b). Hence, there has been the probability of fluctuation in brightness of the fluorescent display cell 8b between a case of both the data electrodes 10a and 10b being turned ON and the other case of only the data electrode 10b being turned ON. There has also been the probability of such difference in brightness, though slightly, from the tolerance of assembling such as positioning of the electrodes or from the fluctuation of an input voltage.
Further, while the data signals D1 to D4 and scanning signals S1 to S4 as shown in FIG. 4 are being applied to the data electrodes 10 and the scanning electrodes 12 as shown in FIG. 6 and FIG. 7, if the polarities of adjoining sets of the electrodes 10 and 12 are as shown in FIG. 9, then the thermoelectrons emitted from one of the cathodes 4 flow normally as indicated by the arrow P, pass through the opening 15 in the control electrode 14, and bombard the predetermined fluorescent display cell 8 to cause it to emit light. However, there has been the probability of a portion of the emitted thermoelectrons flowing also in the direction of the arrow Q and straying into other adjoining openings 15, whereby other than the predetermined fluorescent display cells 8 are caused to emit false light.
Furthermore, there has been the probability of the electric field of a high voltage of the anode 8a penetrating through the gap between the frame body 1b and the planar electrode 14 and reaching the vicinity of the cathode 4, thereby causing electrons emitted from the cathode 4 to pass through the gap and reach the fluorescent display cells 8 at the circumference of the display screen 1a and cause them to emit false light.